1. Field of the Invention
This invention relates to ionized-gas lasers. More specifically, this invention relates to altering the magnetic field profile in or near the cathode transition region of an ionized-gas laser.
2. Description of Related Art
An ionized-gas laser or ion laser is a type of laser, characterized by ionization of a gas and electrical discharge through that gas. Magnetic confinement of the gas, typically by a coaxially oriented electromagnetic solenoid, is often used to concentrate charged particles in the region of an arc discharge through the gas. As used herein, "magnetic confinement" means concentration of charged particles by means of a magnetic field. As is well known in the art, certain gases will exhibit population inversion under such circumstances, and will lase. As is also well known in the art, noble gases such as Neon, Argon, Krypton and Xenon are preferred for the operation of ion lasers of the type disclosed herein, but it will become clear to one of ordinary skill in the art, after perusal of the specification, drawings and claims herein, that other gases may also be incorporated in an embodiment of the invention, and the use of other gases does not lie outside the concept and scope of the invention.
Ion lasers and their operation, as well as other lasers of substantial applicability, are fully disclosed in section 2, volume 2 of the 1982 edition of the CRC Handbook of Laser Science and Technology (and references cited therein), each hereby incorporated by reference as if fully set forth herein. A detailed description of ion lasers would be well known to one of ordinary skill in the art, and accordingly is not repeated herein.
A typical ion laser may comprise a cathode and an anode for respectively sourcing and sinking charged particles through an ionized gas contained in a discharge volume, and a solenoid electromagnet for generating a coaxially aligned magnetic field for concentrating and aiding confinement of the ionized gas in a narrow, substantially cylindrical region of the discharge volume. In normal operation, currents of up to 65 amperes at 40 kilowatts of input power are typical. A glow discharge near the cathode is confined by a substantially cone-shaped region near the cathode (commonly called the "cathode transition region" or the "cathode throat region") and compressed into an arc discharge in an active region of the discharge volume. The arc discharge continues through the ionized gas to a region near the anode. While total current flow remains the same, the current density changes substantially in the cathode transition region. Similarly, there may also be an anode transition region near the anode.
In a typical ion laser, the arc discharge of the gas has high electrical and thermal conductivity. A large amount of heat is generated in the arc discharge and must therefore be dissipated somehow. Although there are a number of known methods for dissipation of such heat, two typical methods are as follows: (1) Heat may be dissipated to the structural walls which confine the gas by means of a plurality of thermally conductive disks placed parallel to each other and disposed across and around the arc discharge path. The center of each such disk may have a hole to allow the arc discharge to pass through without interference; these holes are typically largest near the cathode, successively smaller in the cathode transition region, and smallest in the main body of the discharge volume of the laser. (2) The structural walls may comprise a thermally conductive ceramic in direct thermal contact with the arc discharge. A discharge volume defined by such structural walls may be substantially similar to that defined by the thermally conductive disks of the first method above. These features are well known in the art and are consequently not described in detail herein.
In a typical ion laser, the cathode transition region may be subject to excessive sputtering of the material defining the cathode transition region, e.g. the thermally conductive disks or thermally conductive ceramic as noted above. High thermal stress and thermal loading in this region are also typical. These effects can cause a tendency toward local erosion of any materials placed near the cathode transition region, thus reducing the useful life of the ion laser itself.
A typical ion laser may also exhibit low efficiency in converting input electrical power into output laser light. At a constant discharge current, the efficiency of the laser is inversely proportional to the voltage across the discharge volume, so any method for reducing such voltage while maintaining output power is advantageous. Efficiency may be of interest with respect to certain regions of the electromagnetic spectrum, e.g. output visible light and output ultraviolet light. A typical ion laser may also exhibit substantial optical noise in its output, possibly arising from fluctuations of plasma density, temperature, and other parameters, within the discharge volume.
Known solutions to one or the other of these sets of problems include (1) longitudinal adjustment of the external position of a single coaxial solenoid winding which comprises the electromagnetic solenoid, (2) adjustment of the pressure of the ionized gas, (3) reducing the length of the discharge volume and/or (4) enlarging the diameter of the discharge volume. While these methods of the prior art may achieve some success, they are not completely satisfactory because they do not achieve the dramatic effect of this invention, and because they are generally unable to solve more than one problem at a time. Each prior art solution noted above typically achieves only minor reduction of the sputtering, thermal stress and thermal loading problems noted above, and may also reduce the efficiency of the laser. Accordingly, there is a need for an improved ion laser which addresses all of the problems noted above simultaneously.